The invention relates to a sensor for magnetic-inductive flowmeters in which a sensing tube equipped with sensing electrodes is disposed within a steel housing. Two magnetic coils are mounted on the tube opposite from one another. Each coil has a bolt-shaped or cylindrical core fitted with a flange-like base and engages an outer wall of the measuring tube. The other end of the core is affixed to the housing. The coil further includes a dielectric winding bobbin.
In a known sensor of this kind wire is coiled about the bobbin and the bobbin with the wire is then slipped over the core. The coil is fixedly mounted to the steel housing and the bobbin is secured against axial shifting by positioning a take-up washer between the bobbin and a cover plate carried by the core. The coil is secured with a snap ring in an annular groove of the steel housing. Such a mounting of the coil requires multiple parts, results in a relatively unwieldily construction and high costs, and is unsuited for use on automatic assembly lines.
An object of the present invention is thus to devise a sensor of this kind that is of a simple construction and facilitates its assembly so that, when needed, it can be carried out by robots and/or an automatic assembly line.
The present invention achieves this object by providing the core with a flange affixed to its upper end and by constructing the bobbin of two semi-cylindrical halves which extend about the core, and on which the conductor wire is wound.
Preferably, the flange is integrally formed with the core by casting both together. In this manner the prefabricated core can be attached to the steel housing by welding of the like.
Given such a core construction, the bobbin can no longer be axially slipped over the core. Hence, the bobbin is longitudinally split so that both semicylindrical halves or components can be applied to the core by moving them in a radial direction towards the core. The conductor wire is then wound around the bobbin after the latter has been placed over the core. A particularly good magnetic grounding of both magnetic coils is achieved through the flange which is in direct contact with the steel housing.
The core flange is preferably formed of two integrally cast, diametrically opposite webs the outer ends of which include areas which are formed to engage the steel housing. These areas establish a tight fit and are welded to the housing. The two halves of the bobbin are attached to the core by providing them with partially overlapping end flanges which are secured to each other with a spring catch or the like. The outer, cylindrical winding surface of the bobbin has guide grooves which facilitate a tightly packed winding of the conductor wire. This also enhances the sensing characteristic of the instrument. One end flange of the bobbin, which is preferably constructed of plastic material, has two wire clamps for receiving and attaching the ends of the conductor wire. This allows for a more precise positioning and fixing of the wire on the bobbin.
An embodiment of the invention is shown in the drawings.